In the spring of 1964 a central dialysate supply system, capable of supplying fluid to the dialyzers of several patients at the same time, was placed in operation at the University of Washington Hospital in Seattle. Because of the trend toward the establishment of dialysis centers in which several patients are treated simultaneously, it was believed that important advantages could be achieved through the use of such a device in place of individual dialysate reservoir tanks. Instead of cleaning and sterilizing a dialysis tank for each treatment, equipment preparation could be performed once for a nuniber of dialyses, thereby reducing labor. Less space would be required in the maintenance laboratory and in the dialysis room because of the elimination of the individual tanks. Capital investment per patient would diminish as the number of patients in the dialysis center increased. The noise level in the dialysis room would be reduced to provide a more pleasant atmosphere. If desired, the entire unit could be located in an adjacent area to further reduce the noise. The central system was designed to supply dialysate for from 1–15 simultaneous dialyses at a dialysate flow of 500 ml./min. through each dialyzer. It was also equipped to provide dialysis fluid at 37°C single pass as suggested by the experimental work of Fry and Hoover(1) in which they showed this condition to be more efficient than 20° recirculation dialysis. The duration of single pass dialysis would not be limited by the size of a reservoir. At the 1964 meeting of the American Society for Artificial Internal Organs a preliminary report on the design and initial use of the system was given(2). The following report summarizes our experience during the first year of operation. The central fluid supply concept was based on the belief that all patients with chronic uremia could undergo dialysis against a standard bath. This has been successfully demonstrated with the exception of one component. It has been necessary to individualize the potassium according to the requirements of the individual patients. This is accomplished by using a small constant speed roller pump to deliver a small amount of potassium in solution to the dialyzers of those patients who require it.